Crude glyceride oils, particularly vegetable oils, are refined by a multi-stage process, the first step of which is degumming by treatment typically with water or with a chemical such as phosphoric acid, citric acid or acetic anhydride. Gums may be separated from the oil at this point or carried into subsequent phases of refining. A broad range of chemicals and operating conditions have been used to perform hydration of gums for subsequent separation. For example, Vinyukova et al., "Hydration of Vegetable Oils by Solutions of Polarizing Compounds," Food and Feed Chem., Vol. 17-9, pp. 12-15 (1984), discloses using a hydration agent containing citric acid, sodium chloride and sodium hydroxide in water to increase the removal of phospholipids from sunflower and soybean oils.
After degumming, the oil may be refined by a chemical process including neutralization, bleaching and deodorizing steps. Alternatively, a physical process may be used, including a pretreating and bleaching step and a steam refining and deodorizing step. State-of-the-art processes for both physical and chemical refining are described by Tandy et al. in "Physical Refining of Edible Oil," J. Am. Oil Chem. Soc., Vol. 61, pp. 1253-58 (July 1984).
An object of either refining process is to reduce the levels of contaminants, including free fatty acids, phosphorus (typically as phospholipids), metal ions, soaps and color bodies or pigments, which can lend off colors, odors and flavors to the finished oil product. Ionic forms of the metals calcium, magnesium, iron and copper are thought to be chemically associated with free fatty acids and to negatively effect the quality and stability of the final oil product. Free fatty acids are conventionally removed by means of caustic refining as well as steam distillation under reduced pressure.
One widespread use of glyceride oils is for frying food items. The continuous use of deep fat fryers, however, causes the oil to become depleted and contaminated. Spent frying oil from a deep fat fryer contains various particulate and nonparticulate contaminants. Parts of the food product break off during frying and remain in the cooking oil. Many food products are coated with a seasoned coating prior to immersion in the frying oil, and particles of the coating break free from the product and remain in the cooking oil. In addition, fats, blood, etc., from the food product itself will be extracted into the frying oil and may undergo degradation during the frying process. Extraction of fat into the oil contaminates the oil with some of the same compounds which must be removed from crude glyceride oils during initial refining: phospholipids, metal ions, FFAs, etc.
It is customary in fast food restaurants to filter particulate matter from the frying oil at the end of the day. Merely filtering the spent frying oil will only remove particulate contaminants. Phospholipids, FFAs, metal ions and color bodies remain in the filtered oil. Accordingly, an object of the present invention to provide a process for reclaiming spent glyceride oils by removing contaminants which accumulate in the oil during the frying process.
The removal of free fatty acids from crude and spent edible oils has been the object of a number of previously proposed physical and chemical process steps. For example, U.S. Pat. No. 4,499,196 (Yuki) discloses an adsorbing deacidifier for use in oily substances, wherein the deacidifier comprises dehydrated natural or synthetic zeolites and an aqueous solution of sodium hydroxide or potassium hydroxide adsorbed into the zeolites. U.S. Pat. No. 4,150,045 (Sinha) discloses a method for removing free fatty acids, phospholipids and peroxide compounds from crude vegetable oil using a bed of activated carbon impregnated with magnesium oxide (MgO). U.S. Pat, No. 1,386,471 (Tuttle et al.) discloses the use of alkalized fullers' earth (prepared by shaking fullers' earth with lime water) to remove volatile substances from cacao oil. U.S. Pat. No. 4,913,922 (Hawkes et al.) describes a process for removing free fatty acids using a precoat filter bed containing diatomaceous earth to separate particulates, which stops further release of free fatty acid from breakdown of organic particulates, and then mixing the oil with calcium silicate as the adsorbent for dissolved free fatty acids. U.S. Pat. No. 4,112,129 (Duensing et al.) teaches the utility of a composition for the reduction of the rate of free fatty acid buildup in cooking oils, which consists of diatomite, synthetic calcium silicate hydrate and synthetic magnesium hydrate. U.S. Pat. No. 4,764,384 (Gyann) describes treating spent cooking oil with a filtering media consisting of synthetic amorphous silica, synthetic amorphous magnesium silicate, diatomaceous earth, and synthetic amorphous silica-alumina. It is disclosed that synthetic amorphous silica alone will not be an efficient filtering media, but that additional materials are necessary for removal of free fatty acids and proper bleaching, as well as to achieve adequate flow rates through the filter.